An electroluminescent device is one type of self-luminescent-type display devices, and has advantages in that it has a wide viewing angle, an excellent contrast, and quick response time.
An organic light emitting device has a structure in which an organic thin film is disposed between two electrodes. When voltage is applied to an organic light emitting device having such a structure, light emits by electrons and holes injected from the two electrodes being dissipated after the electrons and holes make a pair by bonding in the organic thin film. The organic thin film may be formed as a monolayer or a multilayer as necessary.
Materials of an organic thin film may have a light emitting function when necessary. For example, as the material of an organic thin film, compounds capable of forming a light emitting layer alone may be used, or compounds capable of performing as a host or a dopant of a host-dopant-based light emitting layer may also be used. In addition to these, compounds capable of performing hole injection, hole transfer, electron blocking, hole blocking, electron transfer, electron injection, or the like, may also be used as the material of an organic thin film.
There have been continuous demands for the development of organic thin film materials in order to improve the performance, life span or efficiency of an organic light emitting device.
For example, CBP has been mostly widely known so far as a host material of a phosphorescent light emitting body, and an organic light emitting device in which a hole blocking layer such as BCP and BAlq is applied, and an organic light emitting device in which BAlq derivatives are used as a host are well known.
However, existing materials have advantages in the aspect of light emitting properties, but have disadvantages such that the materials change when going through a high-temperature deposition process under vacuum due to a low glass transition temperature and very low thermal stability. In an organic light emitting device, power efficiency=(n/voltage)×current efficiency, therefore, power efficiency is inversely proportional to voltage, and power efficiency needs to be high in order to have low power consumption of the organic light emitting device. In fact, an organic light emitting device that uses a phosphorescent light emitting material has quite high current efficiency (cd/A) compared to an organic light emitting device that uses a fluorescent light emitting material, however, when existing materials such as CBP or BAlq are used as the host of a phosphorescent light emitting material, there are no huge advantages in terms of power efficiency (lm/w) since driving voltage is high compared to that of an organic light emitting device using a fluorescent material. In addition, the life span of an organic light emitting device is not at all satisfactory, therefore, there have been demands for the development of host materials that are more stable and show more excellent performances.